The present invention relates to filter materials with adsorptive properties and to a method for their manufacture. Likewise, the present invention has as its subject matter adsorption filters which consist of at least two layers of these filter materials.
In the state of the art a variety of filter materials are known. For example, bulk filters are known, in which the filter material consists of a loose bulk of adsorption materials which necessarily must be held together by a housing or container. These classical bulk filters have a series of to some extent serious disadvantages. This is because there are limitations on the selection of the particle size in that if the adsorbent particles are of too small a diameter they offer too high a resistance to flow, and on the other hand too large a particle diameter results in poor adsorption kinetics. Since the adsorption material is present in the form of loose bulk material, breakthroughs regularly occur. Also, as a result of vibration or shaking in the use of such bulk filters, adsorption material can be lost through abrasion.
Attempts are made to get around these disadvantages of conventional bulk filters by making so-called sheet filters which consist of an air-permeable support material to which first a glue must be applied, discontinuously and generally in the form of dots or lines, onto which the adsorbent particles are then affixed. The air-permeable support material can be woven or knit goods, or also an open-pore, reticulated polyurethane foam. The disadvantage of these sheet filters lies in their generally expensive manufacture and in their not always sufficient stability of shape. Also, in their manufacture and in their subsequent use, a bad odor is produced time and again especially due to degradation products or solvent components of the glues used.